1. Field of the Invention
This invention relates to a polyhydroxyalkanoate (hereinafter, referred to as a “PHA”) synthase, a gene encoding the synthase, a recombinant vector containing the gene, a transformant transformed by the vector, a process for producing the PHA synthase utilizing the transformant, and a process for preparing the PHA utilizing the transformant.
2. Related Background Art
There have been reported a number of microorganisms producing poly-3-hydroxybutyric acid (PHB) or another PHA and storing it therein (“Biodegradable Plastic Handbook”, edited by Biodegradable Plastic Research Society, NTS Co. Ltd., p. 178-197 1995). These polymers may be, as conventional plastics, used for producing a variety of products by, for example, melt-processing. Since they are biodegradable, they have an advantage that they can be completely degraded by microorganisms in the natural environment, and they do not cause pollution due to remaining in the natural environment like many conventional polymer compounds. Furthermore, they are excellently biocompatible, and thus are expected to be used in applications such as a medical soft member.
It is known that a composition and a structure of such a PHA produced by a microorganism may considerably vary depending on the type of a microorganism used for the production, a culture-medium composition and culturing conditions. Investigations have been, therefore, mainly focused on controlling such a composition or structure for the purpose of improving physical properties of a PHA.
For example, Japanese Patent Application Nos. 7-14352 and 8-19227 and Japanese Examined Publication No. 6-15604 describe that Alcaligenes eutropus H16 (ATCC No. 17699) and its variants may produce 3-hydroxybutyric acid (3HB) and its copolymer with 3-hydroxyvaleric acid (3HV) with various composition ratios by changing a carbon source during culturing.
Japanese Patent Publication No. 2642937 has disclosed that PHA in which a monomer unit is 3-hydroxyalkanoate with 6 to 12 carbon atoms may be produced by supplying a non-cyclic aliphatic hydrocarbon as a carbon source to Pseudomonas oleovorans (ATCC No. 29347).
Japanese Patent Application Laid-Open No. 5-7492 discloses methods in which Methylobacterium sp., Paracoccus sp., Alcaligenes sp., and Pseudomonas sp. are contacted with a primary alcohol with 3 to 7 carbon atoms to produce a copolymer of 3HB and 3HV.
Japanese Patent Application Laid-Open No. 5-93049 and No. 7-265065 have disclosed that Aeromonas caviae is cultured using oleic acid or olive oil as a carbon source to produce a two-component copolymer of 3HB and 3-hydroxyhexanoic acid (3HHx).
Japanese Patent Application Laid-Open No. 9-191893 has disclosed that Comamonas acidovorans IF013852 is cultured using gluconic acid and 1,4-butanediol as carbon sources to produce a polyester having 3HB and 4-hydroxybutyric acid as monomer units.
Furthermore, it has been reported that certain microorganisms produce PHAs having a variety of substituents such as groups derived from an unsaturated hydrocarbon, ester, allyl, cyano, groups derived from a halogenated hydrocarbon and epoxide. Recently, there have been attempts for improving physical properties of a PHA produced by a microorganism using such a procedure.
As an example of such a polymer, a PHA having a phenyl group in its side chain has been developed. For example, Makromol. Chem., 191, 1957-1965 (1990); Macromolecules, 24, 5256-5260 (1991); and Chirality, 3, 492-494 (1991) have described production of a PHA comprising 3-hydroxy-5-phenylvaleric acid (3HPV) as a monomer unit by Pseudomonas oleovorans, where there has been observed variation in polymer physical properties probably due to the presence of 3HPV.
As described above, microorganism-produced PHAs with various combinations of composition and structure have been obtained by varying factors such as the type of a microorganism used, a culture medium composition and culturing conditions. However, each microorganism or PHA synthase has significantly different substrate specificity. Therefore, it has been difficult to produce PHAs comprising different monomer units extensively suitable to a variety of applications using known microorganisms or PHA synthases alone.